Jessica Duggan grew up in this starchy historic city in the 1990′s. She remembers field trips with her mother to the historic Battery neighborhood, watching tourists “doing the horse thing and the market thing.” She dreamed of staying here as an adult. But she had to admit that her hometown was hopelessly uncool.

Fast-forward more than a decade and you’d hardly recognize the place. A booming tech start-up economy and a thriving arts and restaurant scene have helped this old Civil War tourist magnet do something that places across the USA have been trying to do for decades: attract young, college-educated workers and keep them there as they start families. The mild weather and easy access to nearly 200 miles of beaches don’t exactly hurt.

“I always knew I wanted to end up here,” says Duggan, 23. “It becoming cooler is a plus.”

Charleston now teems with college-educated young people, 20- and 30-somethings who have come for the jobs and stayed for the lifestyle. New bars and restaurants seem to open weekly. Average commute times hover around 10 minutes. At the gas station on the way home, you can fill your growler with craft-brewed beer.

This is a new kind of city, born of deep demographic shifts and the power of technology. Where traditional college towns have long attracted young people who get an education and then leave, another kind of town is emerging: the post-college town.

Charleston is one of the smaller cities in this emerging brand of urban center. It joins larger ones such as Seattle, San Francisco, Boston, Minneapolis and Washington, D.C. They’re 20-something magnets that don’t just survive but thrive. Among those with the highest ratio, several are old-fashioned cities such as Charleston, and Alexandria, Va., places designed before automobiles arrived. Several of the most popular cities have become an important part of New Urbanism, which models development around mixed-use development and pedestrian-friendly spaces.

“These places seem to be built for people, not for automobiles,” says University of Nevada-Las Vegas demographer Robert Lang. “And the 20-somethings love the people, not the automobile.”

Using recent U.S. Census data, USA TODAY has identified 289 cities that have more 20-somethings than teens — in the case of Charleston and about a dozen other cities, it’s 2-to-1 or higher.

The higher the ratio, the stronger the local pull for young adults. That’s key, because city residents who are ages 10 to 19 mostly grew up there. But those who are 20 to 29 are much more likely to have moved to a city to attend college, follow a boyfriend or girlfriend, get married or relocate for a job. A high ratio is also an indicator that many young people simply never left.

MILLENNIAL MAGNETS

Some cities have become strong magnets for young adults. For cities over 100,000 people, ratio shows the number of people ages 20 to 29 for every 100 teens. U.S. ratio = 103 to 100.

NAME

TOTAL POP., 2012

PEOPLE 20-29 PER 100 TEENS

Arlington, Va.

209,077

344

Cambridge, Mass.

105,026

303

Alexandria, Va.

140,337

284

Gainesville, Fla.

124,981

241

San Francisco

807,755

239

Seattle

612,916

232

Provo, Utah

113,105

223

Boston

619,662

214

Fargo, N.D.

106,005

210

Madison, Wisc.

234,586

210

Tallahassee

181,821

209

Tempe, Ariz.

164,139

207

Norfolk, Va.

243,056

203

Charleston, S.C.

120,903

197

Knoxville, Tenn.

179,973

195

Minneapolis

385,023

195

Orlando

240,185

192

Richmond, Va.

205,348

192

Washington

605,759

191

Springfield, Mo.

160,246

188

Austin

799,939

186

Columbia, Mo.

109,008

185

Berkeley, Calif.

112,662

183

Denver

604,356

181

Salt Lake City

186,740

181

Ann Arbor, Mich.

114,725

180

Atlanta

425,931

177

Pittsburgh

306,430

176

Jersey City

248,435

175

Portland, Ore.

585,888

175

Athens-Clarke County, Ga.

116,353

171

Everett, Wash.

103,135

171

Fort Collins, Colo.

144,329

171

Murfreesboro, Tenn.

109,172

171

Lansing, Mich.

114,537

170

Columbus, Ohio

790,168

167

Norman, Okla.

111,753

165

Nashville-Davidson, Tenn.

605,859

164

Costa Mesa, Calif.

110,322

160

Denton, Texas

115,098

160

Killeen, Texas

127,995

160

Lincoln, Neb.

259,218

156

Lubbock, Texas

229,428

156

Columbia, S.C.

129,757

155

Eugene, Ore.

156,222

155

Savannah, Ga.

137,690

155

Wilmington, N.C.

107,116

155

Honolulu

341,727

154

Cincinnati

297,314

153

Fayetteville, N.C.

200,439

153

Lexington-Fayette, Ky.

296,766

153

Abilene, Texas

118,484

152

Enterprise, Nev.

113,150

152

Miami, Fla.

401,927

152

Durham, N.C.

229,963

151

Pasadena, Calif.

137,316

151

San Diego

1,308,619

151

Spring Valley CDP, Nev.

178,673

151

St. Louis

318,527

151

Sunnyvale, Calif.

141,123

150

Baton Rouge

229,174

149

Clarksville, Tenn.

133,583

149

New Haven, Conn.

129,898

148

New Orleans

341,407

146

Metairie, La.

138,369

145

Sioux Falls, S.D.

154,526

145

Grand Rapids, Mich.

189,340

144

Chicago

2,702,471

143

Baltimore

620,644

142

Daly City, Calif.

101,538

142

Spokane, Wash.

208,701

142

Evansville, Ind.

119,226

141

Lafayette, La.

120,757

140

Raleigh, N.C.

405,007

140

Paradise CDP, Nev.

220,202

139

Birmingham, Ala.

213,180

138

Dallas

1,207,202

138

Fort Lauderdale

167,370

138

New York

8,199,221

138

Santa Clara, Calif.

116,301

138

Bellevue, Wash.

122,873

137

Newport News, Va.

180,831

136

Philadelphia

1,525,811

136

Little Rock

193,691

135

Rochester, N.Y.

210,967

135

St. Paul

286,171

135

Oakland

392,890

134

Chattanooga, Tenn.

167,869

133

Hayward, Calif.

145,165

133

Irving, Texas

217,021

132

Reno

226,305

132

Stamford, Conn.

122,878

132

Wichita Falls, Texas

104,152

132

Boise

208,332

131

Manchester, N.H.

109,786

131

Waco, Texas

124,843

131

Greensboro, N.C.

270,619

130

Houston

2,107,449

130

Lakewood, Colo.

143,496

130

Rochester, Minn.

106,903

130

Tucson

521,695

130

Kansas City, Mo.

459,772

128

Sacramento

467,467

128

Brandon, Fla.

102,555

127

Los Angeles

3,804,503

127

Oklahoma City

581,094

127

Augusta-Richmond County, Ga.

195,646

126

Des Moines

204,362

126

Lowell, Mass.

106,739

126

Providence

178,185

126

Albuquerque

545,083

124

Buffalo

261,955

124

Charlotte

740,931

124

Elizabeth, N.J.

124,795

124

Fullerton, Calif.

135,419

124

Hampton, Va.

137,471

124

Huntsville, Ala.

179,855

124

Independence, Mo.

116,513

124

Clearwater, Fla.

108,138

123

Syracuse, N.Y.

144,703

123

Billings, Montana

104,374

122

Indianapolis

822,006

122

Tacoma, Wash.

200,013

122

Worcester, Mass.

181,473

122

Anchorage

291,470

121

Green Bay, Wisc.

104,226

121

Jacksonville

823,652

121

Oceanside, Calif.

167,799

121

Omaha

412,689

121

Tampa

339,391

121

Tulsa

391,486

121

Virginia Beach, Va.

439,528

121

Glendale, Calif.

192,537

120

Cedar Rapids, Iowa

126,921

119

Peoria, Ill.

114,754

119

Pompano Beach, Fla.

100,819

119

Richardson, Texas

100,057

119

Westminster, Colo.

106,750

119

Concord, Calif.

122,683

118

Erie, Pa.

101,454

117

Milwaukee

594,328

117

Toledo, Ohio

287,487

117

Newark

276,478

116

Orange, Calif.

136,891

116

Salem, Ore.

154,835

116

Shreveport, La.

200,099

116

Springfield, Ill.

115,982

116

Topeka

127,312

116

Bridgeport, Conn.

144,446

115

Richmond, Calif.

104,225

115

Vancouver, Wash.

162,699

115

Wichita, Kansas

381,176

115

Hialeah, Fla.

226,837

114

Memphis, Tenn.

651,050

114

Mobile, Ala.

195,239

114

St. Petersburg, Fla.

245,363

114

Akron, Ohio

199,955

113

Colorado Springs

417,534

113

Fairfield, Calif.

105,407

113

Long Beach

463,589

113

Montgomery, Ala.

205,516

113

Aurora, Colo.

326,249

112

Burbank, Calif.

103,420

112

Huntington Beach, Calif.

191,403

112

San Jose

954,379

112

Santa Rosa, Calif.

167,207

112

Irvine, Calif.

213,880

111

Paterson, N.J.

145,655

111

Mesa, Ariz.

443,875

110

Midland, Texas

112,618

110

Scottsdale, Ariz.

219,867

110

Winston-Salem, N.C.

230,030

110

Yonkers, N.Y.

196,459

110

Arlington, Texas

367,154

109

Beaumont, Texas

117,769

109

Dayton, Ohio

142,670

109

Gresham, Ore.

105,612

109

Oxnard, Calif.

197,456

109

San Antonio

1,335,287

109

Allentown, Pa.

117,942

108

El Monte, Calif.

114,032

108

Louisville-Jefferson County, Ky.

597,231

108

Fresno, Calif.

495,777

107

Odessa, Texas

101,545

107

South Bend, Ind.

101,282

107

West Valley City, Utah

129,123

107

Hollywood, Fla.

142,060

106

Jackson, Miss.

174,382

106

Santa Ana, Calif.

326,608

106

Amarillo, Texas

191,118

105

Fort Worth, Texas

743,865

105

Sterling Heights, Mich.

129,887

105

Vallejo, Calif.

116,417

105

Escondido, Calif.

144,311

104

Corpus Christi, Texas

305,427

103

Hartford, Conn.

124,879

103

Kansas City, Kansas

145,605

103

Riverside, Calif.

306,128

103

Anaheim, Calif.

337,471

102

Cleveland, Ohio

397,972

102

Columbus, Ga.

191,278

102

Phoenix

1,462,368

102

San Buenaventura (Ventura), Calif.

106,273

102

Chandler, Ariz.

237,456

101

Las Vegas

587,699

101

Pueblo, Colo.

106,944

101

Thornton, Colo.

118,747

101

East Los Angeles, Calif.

126,751

100

Fort Wayne, Ind.

253,617

100

Glendale, Ariz.

229,331

100

Inglewood, Calif.

110,225

100

Kent, Wash.

108,700

100

Rockford, Ill.

152,948

100

Columbia, Md.

100,735

99

Miami Gardens, Fla.

107,884

99

Garden Grove, Calif.

171,377

98

Salinas, Calif.

150,634

98

Waterbury, Conn.

110,074

98

Carrollton, Texas

120,727

97

Modesto, Calif.

201,986

97

Overland Park, Kansas

174,503

97

Rancho Cucamonga, Calif.

165,775

97

Pomona, Calif.

149,431

96

Sunrise Manor, Nev.

190,931

96

West Covina, Calif.

106,290

96

Fremont, Calif.

215,188

95

Round Rock, Texas

100,764

95

Warren, Mich.

134,550

95

Bakersfield, Calif.

347,091

94

Elgin, Ill.

109,513

94

Flint, Mich.

103,263

94

Springfield, Mass.

153,278

93

Visalia, Calif.

123,905

93

Ontario, Calif.

165,260

92

West Jordan, Utah

103,846

92

Grand Prairie, Texas

174,631

91

Norwalk, Calif.

105,603

91

Henderson, Nev.

258,270

90

Pasadena, Texas

149,506

90

Stockton, Calif.

292,262

90

Antioch, Calif.

102,575

89

Aurora, Ill.

196,569

89

Carlsbad, Calif.

105,097

89

El Paso

650,778

89

Olathe, Kansas

125,902

89

Arvada, Colo.

106,965

88

Downey, Calif.

111,807

88

Pembroke Pines, Fla.

155,578

88

Torrance, Calif.

145,443

88

Chesapeake, Va.

223,233

87

Roseville, Calif.

119,537

87

Fontana, Calif.

196,129

86

Garland, Texas

227,641

86

Miramar, Fla.

121,447

86

Chula Vista, Calif.

242,499

85

Joliet, Ill.

147,098

85

McAllen, Texas

130,297

85

Detroit

721,459

84

Lancaster, Calif.

155,496

84

Mesquite, Texas

139,615

84

Plano, Texas

263,122

84

Simi Valley, Calif.

123,942

84

North Las Vegas, Nev.

215,762

83

Rialto, Calif.

100,009

83

San Bernardino, Calif.

210,624

83

High Point, N.C.

104,394

82

Moreno Valley, Calif.

193,758

82

Corona, Calif.

153,644

81

Peoria, Ariz.

154,566

81

Santa Clarita, Calif.

175,922

81

Cary, N.C.

136,627

78

Laredo, Texas

236,063

77

Palm Bay, Fla.

102,814

77

Port St. Lucie, Fla.

163,748

77

Palmdale, Calif.

151,841

75

Victorville, Calif.

115,069

73

Cape Coral, Fla.

155,405

72

Brownsville, Texas

175,210

71

McKinney, Texas

131,882

71

Coral Springs, Fla.

122,219

70

Gilbert, Ariz.

208,850

70

Surprise, Ariz.

115,007

70

Murrieta, Calif.

102,345

69

Temecula, Calif.

100,621

69

Centennial, Colo.

101,339

68

Thousand Oaks, Calif.

126,570

68

Elk Grove, Calif.

151,639

67

Frisco, Texas

116,944

61

Naperville, Ill.

142,143

56

For Duggan, it’s the latter. She attended the College of Charleston and graduated in 2011. At 23, she’s already married — she and her husband have an English bulldog named Winston, and she’s editorial director at BiblioLabs, a small tech start-up that designs easy-to-navigate e-book lending websites for public libraries. The company, founded eight years ago, employs 30 people, many of them software engineers. The median age hovers in the mid-20s, and several of her colleagues also say they’re here to put down roots.

WHERE THERE ARE JOBS …

Alex Summer, a software developer from Newberry, S.C., bought a three-bedroom house in suburban Mount Pleasant in 2009, and jokes that he’s “settling down” at age 27.

“You’ve got the beach; you’ve got the history; you’ve got the tech opportunities,” he says. He’s also engaged, so he now hangs out at “the more chill spots” downtown.

Eric Bowman, founder of local software start-up Sparc, says that among his 140 developers, the median age is about 28. And most of them know more than he ever did at that age about software. “These 25-, 27-, 28-year-olds are just blowing me away.” In the past six months nine employees have left to start their own companies in town. “Every one of our developers can get a job in five days,” he says, “so you have to treat your team members fairly.”

Start-ups haven’t been the only ones snapping up educated workers here. Boeing is expanding rapidly. The aerospace giant now assembles 787 Dreamliners at a rate of three a month at a massive facility adjacent to the Charleston airport, and over the next three years it plans to hire about 600 more information technology employees, bringing its total number of workers in the region to about 8,000.

City planners in Alexandria, Va., which ranks third in USA Today’s post-college town ranking, have pushed to integrate commercial development, land use and transit to create a city that allows residents to “live, work and play in the same space,” City Manager Rashad Young says.

When Young thinks of the young professionals in Alexandria, he says he imagines they’re thinking, “I want activity, energy, vitality — I want to be able to get places quickly. I want there to be a concentration of activity that I don’t necessarily have to drive to get to. I want easy access to places and things.”

The demographic change in Charleston has opened up previously sketchy neighborhoods for development, a change that for many locals has been nothing short of breathtaking.

“The whole face of this city has changed in a year-and-a-half,” says David Crowley, a co-owner of The Alley, a popular sports bar that boasts eight lanes of bowling. It’s located in a rapidly changing industrial area about a mile north of downtown, and Crowley says the enterprise would have been unimaginable until recently.

When he attended classes at the College of Charleston a decade ago, “You didn’t go north of Calhoun (Street). It wasn’t safe.” Now he gets so much business most nights he’s got to lease 85 parking spaces from The (Charleston) Post and Courier across the street.

Crowley and his partners built the venue from scratch inside an old liquor-distribution warehouse, and on a recent weekday evening a family with young children rented bowling shoes while a young couple, both of them 31, held a wedding rehearsal dinner in an upstairs event space. In between, an early-evening crowd drank beer, watched live golf on big-screen TVs and played retro coin-operated video games. “They’re in Charleston to live in Charleston,” says Crowley.

WORK, OR KITE-SURF?

Two miles north on Meeting Street, workers are putting the finishing touches on a 13,000-square-foot renovation of the long-vacant 1926 Standard Oil regional headquarters building that soon will be home to about a dozen small creative businesses.

“This is truly what I consider the last frontier of the Charleston peninsula,” says Lindsay Nevin, a young developer who is working with the city to build a “creative corridor” on Meeting Street, an industrial thoroughfare once dominated by car dealerships. It’s already dotted with small artists’ storefronts and independent restaurants. A small-batch distillery recently opened down the street, and Nevin, who bought the abandoned office building last June, has signed three-year leases with, among others, a glass sculptor, a potter, a photographer, a dressmaker, an art magazine and two interior design firms.

Lisa Maki, a co-founder of the tech start-up PokitDok — it helps consumers find low-cost health care providers — says 15 of the company’s 23 employees are based in Charleston. All 15 are software engineers. She calls them “our secret weapon” and says she can hire good engineers here for about half the cost of comparable workers in Silicon Valley. Maki says office space here is “probably a quarter of the price” of comparable space in Silicon Valley.

Many employees want to raise their children in a less high-stress environment, and they love the ability to live close to work, she says. “If the wind comes up, our kite-surfers head to the beach and then get online later. That’s just what they do,” Maki says.

Much of the region’s development owes its success to both public and private investment and upgrades in infrastructure. Government incentives helped to attract and keep companies such as Sparc. Projects such as the 2005 Cooper River Bridge, which connects downtown Charleston and Mount Pleasant, have helped outlying areas thrive. The bridge replaced a pair of notoriously narrow crossings.

The area it helped open up now is home to some of the area’s major employers, including health-tech giant Benefitfocus, which opened in 2000 in a shuttered Walmart. When CEO Shawn Jenkins and a partner started the company, he says, “People were telling me that you could never build a tech company here.” They’re now in the midst of an huge expansion at their headquarters east of downtown, which will add 1,200 more employees by 2015.

The company, which went public last September, develops software that helps employees manage workplace health and life insurance benefits. It has an estimated 20 million users.

“I was always a believer that this town was going to be awesome,” Jenkins says. He jokes that his recruiters often wait till it’s snowing elsewhere in the USA to try tempting prospective workers to visit.

Once they’re at work, his “associates,” as he calls his employees, enjoy coffee from free Starbucks dispensers and Coke machines rigged to dispense drinks for 25 cents. One floor of their campus has been remodeled as a “social work space” that resembles an open-floor loft or a high-end hotel lobby. Hoping to inspire his Web developers to design beautiful stuff, Jenkins has peppered the offices with handsome objects, including a small collection of Fender Stratocaster guitars and, in the middle of one workspace, a gleaming red Ducati 1199 Panigale motorcycle.

Speaking of design, Charleston may be “the single most important city of inspiration to the New Urbanists” who have pushed to redesign cities around more densely populated, pedestrian-friendly living spaces, says Lang, the demographer.

He’s seen it before, in places such as Alexandria, Va., and Savannah, Ga., both of which rank high on USA Todau’s post-college list. ”They’re young and they live in old cities,” says Lang. “Some of America’s oldest cities have the youngest population.”